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Safi R, Menéndez P, Pol A. Lipid droplets provide metabolic flexibility for cancer progression. FEBS Lett 2024; 598:1301-1327. [PMID: 38325881 DOI: 10.1002/1873-3468.14820] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Revised: 01/08/2024] [Accepted: 01/10/2024] [Indexed: 02/09/2024]
Abstract
A hallmark of cancer cells is their remarkable ability to efficiently adapt to favorable and hostile environments. Due to a unique metabolic flexibility, tumor cells can grow even in the absence of extracellular nutrients or in stressful scenarios. To achieve this, cancer cells need large amounts of lipids to build membranes, synthesize lipid-derived molecules, and generate metabolic energy in the absence of other nutrients. Tumor cells potentiate strategies to obtain lipids from other cells, metabolic pathways to synthesize new lipids, and mechanisms for efficient storage, mobilization, and utilization of these lipids. Lipid droplets (LDs) are the organelles that collect and supply lipids in eukaryotes and it is increasingly recognized that the accumulation of LDs is a new hallmark of cancer cells. Furthermore, an active role of LD proteins in processes underlying tumorigenesis has been proposed. Here, by focusing on three major classes of LD-resident proteins (perilipins, lipases, and acyl-CoA synthetases), we provide an overview of the contribution of LDs to cancer progression and discuss the role of LD proteins during the proliferation, invasion, metastasis, apoptosis, and stemness of cancer cells.
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Affiliation(s)
- Rémi Safi
- Josep Carreras Leukemia Research Institute, Barcelona, Spain
- Lipid Trafficking and Disease Group, Institut d'Investigacions Biomèdiques August Pi I Sunyer (IDIBAPS), Barcelona, Spain
| | - Pablo Menéndez
- Josep Carreras Leukemia Research Institute, Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
- Department of Biomedical Sciences, Faculty of Medicine, Universitat de Barcelona, Spain
- Consorcio Investigación Biomédica en Red de Cancer, CIBER-ONC, ISCIII, Barcelona, Spain
- Spanish Network for Advanced Cell Therapies (TERAV), Barcelona, Spain
| | - Albert Pol
- Lipid Trafficking and Disease Group, Institut d'Investigacions Biomèdiques August Pi I Sunyer (IDIBAPS), Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
- Department of Biomedical Sciences, Faculty of Medicine, Universitat de Barcelona, Spain
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2
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Wang J, Kunze M, Villoria-González A, Weinhofer I, Berger J. Peroxisomal Localization of a Truncated HMG-CoA Reductase under Low Cholesterol Conditions. Biomolecules 2024; 14:244. [PMID: 38397481 PMCID: PMC10886633 DOI: 10.3390/biom14020244] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2024] [Revised: 02/07/2024] [Accepted: 02/16/2024] [Indexed: 02/25/2024] Open
Abstract
3-hydroxy-3-methylglutaryl-CoA reductase (HMG-CoA reductase, HMGCR) is one of the rate-limiting enzymes in the mevalonate pathway required for cholesterol biosynthesis. It is an integral membrane protein of the endoplasmic reticulum (ER) but has occasionally been described in peroxisomes. By co-immunofluorescence microscopy using different HMGCR antibodies, we present evidence for a dual localization of HMGCR in the ER and peroxisomes in differentiated human monocytic THP-1 cells, primary human monocyte-derived macrophages and human primary skin fibroblasts under conditions of low cholesterol and statin treatment. Using density gradient centrifugation and Western blot analysis, we observed a truncated HMGCR variant of 76 kDa in the peroxisomal fractions, while a full-length HMGCR of 96 kDa was contained in fractions of the ER. In contrast to primary human control fibroblasts, peroxisomal HMGCR was not found in fibroblasts from patients suffering from type-1 rhizomelic chondrodysplasia punctata, who lack functional PEX7 and, thus, cannot import peroxisomal matrix proteins harboring a type-2 peroxisomal targeting signal (PTS2). Moreover, in the N-terminal region of the soluble 76 kDa C-terminal catalytic domain, we identified a PTS2-like motif, which was functional in a reporter context. We propose that under sterol-depleted conditions, part of the soluble HMGCR domain, which is released from the ER by proteolytic processing for further turnover, remains sufficiently long in the cytosol for peroxisomal import via a PTS2/PEX7-dependent mechanism. Altogether, our findings describe a dual localization of HMGCR under combined lipid depletion and statin treatment, adding another puzzle piece to the complex regulation of HMGCR.
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Affiliation(s)
| | | | | | | | - Johannes Berger
- Department of Pathobiology of the Nervous System, Center for Brain Research, Medical University of Vienna, 1090 Vienna, Austria
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3
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Wang H, Nikain C, Amengual J, La Forest M, Yu Y, Wang MC, Watts R, Lehner R, Qiu Y, Cai M, Kurland IJ, Goldberg IJ, Rajan S, Hussain MM, Brodsky JL, Fisher EA. FITM2 deficiency results in ER lipid accumulation, ER stress, reduced apolipoprotein B lipidation, and VLDL triglyceride secretion in vitro and in mouse liver. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.05.570183. [PMID: 38106013 PMCID: PMC10723279 DOI: 10.1101/2023.12.05.570183] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2023]
Abstract
Objectives Triglyceride (TG) association with apolipoprotein B100 (apoB100) serves to form very low density lipoproteins (VLDL) in the liver. The repertoire of factors that facilitate this association is incompletely defined. FITM2, an integral endoplasmic reticulum (ER) protein, was originally discovered as a factor participating in cytoplasmic lipid droplets (LDs) in tissues that do not form VLDL. We hypothesized that in the liver, in addition to promoting cytosolic LD formation, FITM2 would also transfer TG from its site of synthesis in the ER membrane to nascent VLDL particles within the ER lumen. Methods Experiments were conducted using a rat hepatic cell line (McArdle-RH7777, or McA cells), an established model of mammalian lipoprotein metabolism, and mice. FITM2 expression was reduced using siRNA in cells and by liver specific cre-recombinase mediated deletion of the Fitm2 gene in mice. Effects of FITM2 deficiency on VLDL assembly and secretion in vitro and in vivo were measured by multiple methods, including density gradient ultracentrifugation, chromatography, mass spectrometry, simulated Raman spectroscopy (SRS) microscopy, sub-cellular fractionation, immunoprecipitation, immunofluorescence, and electron microscopy. Main findings 1) FITM2-deficient hepatic cells in vitro and in vivo secrete TG-depleted VLDL particles, but the number of particles is unchanged compared to controls; 2) FITM2 deficiency in mice on a high fat diet (HFD) results in decreased plasma TG levels. The number of apoB100-containing lipoproteins remains similar, but shift from VLDL to LDL density; 3) Both in vitro and in vivo , when TG synthesis is stimulated and FITM2 is deficient, TG accumulates in the ER, and despite its availability this pool is unable to fully lipidate apoB100 particles; 4) FITM2 deficiency disrupts ER morphology and results in ER stress. Principal conclusions The results suggest that FITM2 contributes to VLDL lipidation, especially when newly synthesized hepatic TG is in abundance. In addition to its fundamental importance in VLDL assembly, the results also suggest that under dysmetabolic conditions, FITM2 may be a limiting factor that ultimately contributes to non-alcoholic fatty liver disease (NAFLD) and steatohepatitis (NASH).
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4
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Venkatesan N, Doskey LC, Malhi H. The Role of Endoplasmic Reticulum in Lipotoxicity during Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) Pathogenesis. THE AMERICAN JOURNAL OF PATHOLOGY 2023; 193:1887-1899. [PMID: 37689385 PMCID: PMC10699131 DOI: 10.1016/j.ajpath.2023.08.007] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/14/2023] [Revised: 08/14/2023] [Accepted: 08/18/2023] [Indexed: 09/11/2023]
Abstract
Perturbations in lipid and protein homeostasis induce endoplasmic reticulum (ER) stress in metabolic dysfunction-associated steatotic liver disease (MASLD), formerly known as nonalcoholic fatty liver disease. Lipotoxic and proteotoxic stress can activate the unfolded protein response (UPR) transducers: inositol requiring enzyme1α, PKR-like ER kinase, and activating transcription factor 6α. Collectively, these pathways induce expression of genes that encode functions to resolve the protein folding defect and ER stress by increasing the protein folding capacity of the ER and degradation of misfolded proteins. The ER is also intimately connected with lipid metabolism, including de novo ceramide synthesis, phospholipid and cholesterol synthesis, and lipid droplet formation. Following their activation, the UPR transducers also regulate lipogenic pathways in the liver. With persistent ER stress, cellular adaptation fails, resulting in hepatocyte apoptosis, a pathological marker of liver disease. In addition to the ER-nucleus signaling activated by the UPR, the ER can interact with other organelles via membrane contact sites. Modulating intracellular communication between ER and endosomes, lipid droplets, and mitochondria to restore ER homeostasis could have therapeutic efficacy in ameliorating liver disease. Recent studies have also demonstrated that cells can convey ER stress by the release of extracellular vesicles. This review discusses lipotoxic ER stress and the central role of the ER in communicating ER stress to other intracellular organelles in MASLD pathogenesis.
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Affiliation(s)
- Nanditha Venkatesan
- Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, Minnesota
| | - Luke C Doskey
- Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, Minnesota
| | - Harmeet Malhi
- Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, Minnesota.
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5
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Kumari RM, Khatri A, Chaudhary R, Choudhary V. Concept of lipid droplet biogenesis. Eur J Cell Biol 2023; 102:151362. [PMID: 37742390 PMCID: PMC7615795 DOI: 10.1016/j.ejcb.2023.151362] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Revised: 09/15/2023] [Accepted: 09/18/2023] [Indexed: 09/26/2023] Open
Abstract
Lipid droplets (LD) are functionally conserved fat storage organelles found in all cell types. LDs have a unique structure comprising of a hydrophobic core of neutral lipids (fat), triacylglycerol (TAG) and cholesterol esters (CE) surrounded by a phospholipid monolayer. LD surface is decorated by a multitude of proteins and enzymes rendering this compartment functional. Accumulating evidence suggests that LDs originate from discrete ER-subdomains, demarcated by the lipodystrophy protein seipin, however, the mechanisms of which are not well understood. LD biogenesis factors together with biophysical properties of the ER membrane orchestrate spatiotemporal regulation of LD nucleation and growth at specific ER subdomains in response to metabolic cues. Defects in LD formation manifests in several human pathologies, including obesity, lipodystrophy, ectopic fat accumulation, and insulin resistance. Here, we review recent advances in understanding the molecular events during initial stages of eukaryotic LD assembly and discuss the critical role of factors that ensure fidelity of this process.
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Affiliation(s)
- R Mankamna Kumari
- Lipid Metabolism Laboratory, Department of Biotechnology, All India Institute of Medical Sciences (AIIMS), New Delhi 110029, India
| | - Amit Khatri
- Lipid Metabolism Laboratory, Department of Biotechnology, All India Institute of Medical Sciences (AIIMS), New Delhi 110029, India
| | - Ritika Chaudhary
- Lipid Metabolism Laboratory, Department of Biotechnology, All India Institute of Medical Sciences (AIIMS), New Delhi 110029, India
| | - Vineet Choudhary
- Lipid Metabolism Laboratory, Department of Biotechnology, All India Institute of Medical Sciences (AIIMS), New Delhi 110029, India.
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6
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Safi R, Sánchez-Álvarez M, Bosch M, Demangel C, Parton RG, Pol A. Defensive-lipid droplets: Cellular organelles designed for antimicrobial immunity. Immunol Rev 2023; 317:113-136. [PMID: 36960679 DOI: 10.1111/imr.13199] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/25/2023]
Abstract
Microbes have developed many strategies to subvert host organisms, which, in turn, evolved several innate immune responses. As major lipid storage organelles of eukaryotes, lipid droplets (LDs) are an attractive source of nutrients for invaders. Intracellular viruses, bacteria, and protozoan parasites induce and physically interact with LDs, and the current view is that they "hijack" LDs to draw on substrates for host colonization. This dogma has been challenged by the recent demonstration that LDs are endowed with a protein-mediated antibiotic activity, which is upregulated in response to danger signals and sepsis. Dependence on host nutrients could be a generic "Achilles' heel" of intracellular pathogens and LDs a suitable chokepoint harnessed by innate immunity to organize a front-line defense. Here, we will provide a brief overview of the state of the conflict and discuss potential mechanisms driving the formation of the 'defensive-LDs' functioning as hubs of innate immunity.
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Affiliation(s)
- Rémi Safi
- Lipid Trafficking and Disease Group, Institut d'Investigacions Biomèdiques August Pi I Sunyer (IDIBAPS), Barcelona, Spain
- Josep Carreras Leukemia Research Institute, Barcelona, Spain
| | - Miguel Sánchez-Álvarez
- Centro Nacional de Investigaciones Cardiovasculares (CNIC), Madrid, Spain
- Instituto de Investigaciones Biomédicas Alberto Sols (IIB), Madrid, Spain
| | - Marta Bosch
- Lipid Trafficking and Disease Group, Institut d'Investigacions Biomèdiques August Pi I Sunyer (IDIBAPS), Barcelona, Spain
- Department of Biomedical Sciences, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain
| | - Caroline Demangel
- Immunobiology and Therapy Unit, Institut Pasteur, Université Paris Cité, INSERM U1224, Paris, France
| | - Robert G Parton
- Institute for Molecular Bioscience (IMB), Brisbane, Queensland, Australia
- Centre for Microscopy and Microanalysis (CMM), University of Queensland, Brisbane, Queensland, Australia
| | - Albert Pol
- Lipid Trafficking and Disease Group, Institut d'Investigacions Biomèdiques August Pi I Sunyer (IDIBAPS), Barcelona, Spain
- Department of Biomedical Sciences, Faculty of Medicine, Universitat de Barcelona, Barcelona, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
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7
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Wang J, Han S, Ye J. Topological regulation of a transmembrane protein by luminal-to-cytosolic retrotranslocation of glycosylated sequence. Cell Rep 2023; 42:112311. [PMID: 36972171 PMCID: PMC10520219 DOI: 10.1016/j.celrep.2023.112311] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2022] [Revised: 02/02/2023] [Accepted: 03/11/2023] [Indexed: 03/28/2023] Open
Abstract
Transmembrane proteins must adopt proper topology to perform their functions. We previously demonstrated that ceramide regulates TM4SF20 (transmembrane 4 L6 family 20) by altering the topology of the transmembrane protein, but the underlying mechanism remains obscure. Here we report that TM4SF20 is synthesized in the endoplasmic reticulum (ER) with a cytosolic C terminus and a luminal loop before the last transmembrane helix where N132, N148, and N163 are glycosylated. In the absence of ceramide, the sequence surrounding glycosylated N163 but not N132 is retrotranslocated from lumen to cytosol independent of ER-associated degradation. Accompanying this retrotranslocation, the C terminus of the protein is relocated from cytosol to lumen. Ceramide delays the retrotranslocation process, causing accumulation of the protein that is originally synthesized. Our findings suggest that N-linked glycans, although synthesized in the lumens, may be exposed to cytosol through retrotranslocation, a reaction that may play a crucial role in topological regulation of transmembrane proteins.
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Affiliation(s)
- Jingcheng Wang
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Sungwon Han
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Jin Ye
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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8
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Liu H, Du J, Chao S, Li S, Cai H, Zhang H, Chen G, Liu P, Bu P. Fusobacterium nucleatum Promotes Colorectal Cancer Cell to Acquire Stem Cell-Like Features by Manipulating Lipid Droplet-Mediated Numb Degradation. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2022; 9:e2105222. [PMID: 35170250 PMCID: PMC9035998 DOI: 10.1002/advs.202105222] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2021] [Revised: 12/19/2021] [Indexed: 05/26/2023]
Abstract
Fusobacterium nucleatum is a critical microbe that contributes to colorectal cancer progression and chemoresistance. However, whether and how F. nucleatum regulates colorectal cancer stem-like cells (CCSCs) remains unknown. Here, the authors show that F. nucleatum promotes CCSC self-renewal, and non-CCSCs to acquire CCSC features by manipulating cellular lipid accumulation. F. nucleatum infection decreases lipid accumulation in CCSCs by enhancing fatty acid oxidation, thus promoting CCSC self-renewal. In contrast, F. nucleatum increases lipid accumulation in non-CCSCs by promoting fatty acid formation. Lipids are deposited as lipid droplets, which recruits Numb, a key cell fate regulator, through the AP2A/ACSL3 complex, and MDM2, an E3 ubiquitin ligase, though VCP and UBXD8. On lipid droplets, Numb is degraded by MDM2, activating Notch signaling, thus promoting gain of stem-like cell features. Their findings demonstrate that F. nucleatum directly manipulates colorectal cancer cell fate and reveal the mechanism of lipid droplet-mediated Numb degradation for activating Notch signaling.
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Affiliation(s)
- Haiyang Liu
- Key Laboratory of RNA BiologyKey Laboratory of Protein and Peptide PharmaceuticalInstitute of BiophysicsChinese Academy of SciencesBeijing100101China
| | - Junfeng Du
- Department of General Surgerythe 7th Medical CenterChinese PLA General HospitalBeijing100700China
- The 2nd School of Clinical MedicineSouthern Medical UniversityGuangdong510515China
- Medical Department of General Surgerythe 1st Medical CenterChinese PLA General HospitalBeijing100853China
| | - Shanshan Chao
- Key Laboratory of RNA BiologyKey Laboratory of Protein and Peptide PharmaceuticalInstitute of BiophysicsChinese Academy of SciencesBeijing100101China
- College of Life SciencesUniversity of Chinese Academy of SciencesBeijing100049China
| | - Shuoguo Li
- Center for Biological ImagingInstitute of BiophysicsChinese Academy of SciencesBeijing100101China
| | - Huiyun Cai
- Department of General Surgerythe 7th Medical CenterChinese PLA General HospitalBeijing100700China
| | - Hongjie Zhang
- The core facilityInstitute of BiophysicsChinese Academy of SciencesBeijing100101China
| | - Gang Chen
- Department of General Surgerythe 7th Medical CenterChinese PLA General HospitalBeijing100700China
- Medical Department of General Surgerythe 1st Medical CenterChinese PLA General HospitalBeijing100853China
| | - Pingsheng Liu
- National Laboratory of BiomacromoleculesInstitute of BiophysicsChinese Academy of SciencesBeijing100101China
- Center for Excellence in BiomacromoleculesChinese Academy of SciencesBeijing100101China
| | - Pengcheng Bu
- Key Laboratory of RNA BiologyKey Laboratory of Protein and Peptide PharmaceuticalInstitute of BiophysicsChinese Academy of SciencesBeijing100101China
- College of Life SciencesUniversity of Chinese Academy of SciencesBeijing100049China
- Center for Excellence in BiomacromoleculesChinese Academy of SciencesBeijing100101China
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9
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Abstract
Lipid droplets (LDs) are endoplasmic reticulum-derived organelles that consist of a core of neutral lipids encircled by a phospholipid monolayer decorated with proteins. As hubs of cellular lipid and energy metabolism, LDs are inherently involved in the etiology of prevalent metabolic diseases such as obesity and nonalcoholic fatty liver disease. The functions of LDs are regulated by a unique set of associated proteins, the LD proteome, which includes integral membrane and peripheral proteins. These proteins control key activities of LDs such as triacylglycerol synthesis and breakdown, nutrient sensing and signal integration, and interactions with other organelles. Here we review the mechanisms that regulate the composition of the LD proteome, such as pathways that mediate selective and bulk LD protein degradation and potential connections between LDs and cellular protein quality control.
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Affiliation(s)
- Melissa A Roberts
- Department of Molecular and Cell Biology and Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720, USA;
| | - James A Olzmann
- Department of Molecular and Cell Biology and Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720, USA; .,Chan Zuckerberg Biohub, San Francisco, California 94158, USA
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10
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Ershov P, Kaluzhskiy L, Mezentsev Y, Yablokov E, Gnedenko O, Ivanov A. Enzymes in the Cholesterol Synthesis Pathway: Interactomics in the Cancer Context. Biomedicines 2021; 9:biomedicines9080895. [PMID: 34440098 PMCID: PMC8389681 DOI: 10.3390/biomedicines9080895] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2021] [Revised: 07/20/2021] [Accepted: 07/22/2021] [Indexed: 02/06/2023] Open
Abstract
A global protein interactome ensures the maintenance of regulatory, signaling and structural processes in cells, but at the same time, aberrations in the repertoire of protein-protein interactions usually cause a disease onset. Many metabolic enzymes catalyze multistage transformation of cholesterol precursors in the cholesterol biosynthesis pathway. Cancer-associated deregulation of these enzymes through various molecular mechanisms results in pathological cholesterol accumulation (its precursors) which can be disease risk factors. This work is aimed at systematization and bioinformatic analysis of the available interactomics data on seventeen enzymes in the cholesterol pathway, encoded by HMGCR, MVK, PMVK, MVD, FDPS, FDFT1, SQLE, LSS, DHCR24, CYP51A1, TM7SF2, MSMO1, NSDHL, HSD17B7, EBP, SC5D, DHCR7 genes. The spectrum of 165 unique and 21 common protein partners that physically interact with target enzymes was selected from several interatomic resources. Among them there were 47 modifying proteins from different protein kinases/phosphatases and ubiquitin-protein ligases/deubiquitinases families. A literature search, enrichment and gene co-expression analysis showed that about a quarter of the identified protein partners was associated with cancer hallmarks and over-represented in cancer pathways. Our results allow to update the current fundamental view on protein-protein interactions and regulatory aspects of the cholesterol synthesis enzymes and annotate of their sub-interactomes in term of possible involvement in cancers that will contribute to prioritization of protein targets for future drug development.
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11
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Schumacher MM, DeBose-Boyd RA. Posttranslational Regulation of HMG CoA Reductase, the Rate-Limiting Enzyme in Synthesis of Cholesterol. Annu Rev Biochem 2021; 90:659-679. [PMID: 34153214 DOI: 10.1146/annurev-biochem-081820-101010] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The polytopic, endoplasmic reticulum (ER) membrane protein 3-hydroxy-3-methylglutaryl coenzyme A (HMG CoA) reductase produces mevalonate, the key intermediate in the synthesis of cholesterol and many nonsterol isoprenoids including geranylgeranyl pyrophosphate (GGpp). Transcriptional, translational, and posttranslational feedback mechanisms converge on this reductase to ensure cells maintain a sufficient supply of essential nonsterol isoprenoids but avoid overaccumulation of cholesterol and other sterols. The focus of this review is mechanisms for the posttranslational regulation of HMG CoA reductase, which include sterol-accelerated ubiquitination and ER-associated degradation (ERAD) that is augmented by GGpp. We discuss how GGpp-induced ER-to-Golgi trafficking of the vitamin K2 synthetic enzyme UbiA prenyltransferase domain-containing protein-1 (UBIAD1) modulates HMG CoA reductase ERAD to balance the synthesis of sterol and nonsterol isoprenoids. We also summarize the characterization of genetically manipulated mice, which established that sterol-accelerated, UBIAD1-modulated ERAD plays a major role in regulation of HMG CoA reductase and cholesterol metabolism in vivo.
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Affiliation(s)
- Marc M Schumacher
- Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA;
| | - Russell A DeBose-Boyd
- Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, USA;
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12
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Pagliari F, Marafioti MG, Genard G, Candeloro P, Viglietto G, Seco J, Tirinato L. ssRNA Virus and Host Lipid Rearrangements: Is There a Role for Lipid Droplets in SARS-CoV-2 Infection? Front Mol Biosci 2020; 7:578964. [PMID: 33134318 PMCID: PMC7579428 DOI: 10.3389/fmolb.2020.578964] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Accepted: 09/03/2020] [Indexed: 12/12/2022] Open
Abstract
Since its appearance, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has immediately alarmed the World Health Organization for its very high contagiousness and the complexity of patient clinical profiles. The worldwide scientific community is today gathered in a massive effort in order to develop safe vaccines and effective therapies in the shortest possible time. Every day, new pieces of SARS-CoV-2 infective puzzle are disclosed. Based on knowledge gained with other related coronaviruses and, more in general, on single-strand RNA viruses, we highlight underexplored molecular routes in which lipids and lipid droplets (LDs) might serve essential functions in viral infections. In fact, both lipid homeostasis and the pathways connected to lipids seem to be fundamental in all phases of the coronavirus infection. This review aims at describing potential roles for lipid and LDs in host-virus interactions and suggesting LDs as new and central cellular organelles to be investigated as potential targets against SARS-CoV-2 infection.
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Affiliation(s)
- Francesca Pagliari
- Biomedical Physics in Radiation Oncology, German Cancer Research Center, Heidelberg, Germany
| | - Maria Grazia Marafioti
- Biomedical Physics in Radiation Oncology, German Cancer Research Center, Heidelberg, Germany
| | - Geraldine Genard
- Biomedical Physics in Radiation Oncology, German Cancer Research Center, Heidelberg, Germany
| | - Patrizio Candeloro
- BioNEM Laboratory, Department of Experimental and Clinical Medicine, Magna Graecia University, Catanzaro, Italy
| | - Giuseppe Viglietto
- Department of Experimental and Clinical Medicine, Magna Graecia University, Catanzaro, Italy
| | - Joao Seco
- Biomedical Physics in Radiation Oncology, German Cancer Research Center, Heidelberg, Germany.,Department of Physics and Astronomy, Heidelberg University, Heidelberg, Germany
| | - Luca Tirinato
- Biomedical Physics in Radiation Oncology, German Cancer Research Center, Heidelberg, Germany.,BioNEM Laboratory, Department of Experimental and Clinical Medicine, Magna Graecia University, Catanzaro, Italy
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13
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Wang IH, Huang TT, Chen JL, Chu LW, Ping YH, Hsu KW, Huang KH, Fang WL, Lee HC, Chen CF, Liao CC, Hsieh RH, Yeh TS. Mevalonate Pathway Enzyme HMGCS1 Contributes to Gastric Cancer Progression. Cancers (Basel) 2020; 12:cancers12051088. [PMID: 32349352 PMCID: PMC7281414 DOI: 10.3390/cancers12051088] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2020] [Revised: 04/24/2020] [Accepted: 04/25/2020] [Indexed: 01/26/2023] Open
Abstract
The 3-hydroxy-3-methylglutaryl-CoA synthase 1 (HMGCS1) is a potential regulatory node in the mevalonate pathway that is frequently dysregulated in tumors. This study found that HMGCS1 expression is upregulated in stomach adenocarcinoma samples of patients and tumorspheres of gastric cancer cells. HMGCS1 elevates the expression levels of the pluripotency genes Oct4 and SOX-2 and contributes to tumorsphere formation ability in gastric cancer cells. HMGCS1 also promotes in vitro cell growth and progression and the in vivo tumor growth and lung metastasis of gastric cancer cells. After blocking the mevalonate pathway by statin and dipyridamole, HMGCS1 exerts nonmetabolic functions in enhancing gastric cancer progression. Furthermore, the level and nuclear translocation of HMGCS1 in gastric cancer cells are induced by serum deprivation. HMGCS1 binds to and activates Oct4 and SOX-2 promoters. HMGCS1 also enhances the integrated stress response (ISR) and interacts with the endoplasmic reticulum (ER) stress transducer protein kinase RNA-like endoplasmic reticulum kinase (PERK). Our results reveal that HMGCS1 contributes to gastric cancer progression in both metabolic and nonmetabolic manners.
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Affiliation(s)
- I-Han Wang
- Program in Molecular Medicine, National Yang-Ming University and Academia Sinica, Taipei 112, Taiwan;
- Institute of Anatomy and Cell Biology, School of Medicine, National Yang-Ming University, Taipei 112, Taiwan; (T.-T.H.); (J.-L.C.)
| | - Tzu-Ting Huang
- Institute of Anatomy and Cell Biology, School of Medicine, National Yang-Ming University, Taipei 112, Taiwan; (T.-T.H.); (J.-L.C.)
| | - Ji-Lin Chen
- Institute of Anatomy and Cell Biology, School of Medicine, National Yang-Ming University, Taipei 112, Taiwan; (T.-T.H.); (J.-L.C.)
| | - Li-Wei Chu
- Department and Institute of Pharmacology, School of Medicine, National Yang-Ming University, Taipei 112, Taiwan; (L.-W.C.); (Y.-H.P.); (H.-C.L.)
| | - Yueh-Hsin Ping
- Department and Institute of Pharmacology, School of Medicine, National Yang-Ming University, Taipei 112, Taiwan; (L.-W.C.); (Y.-H.P.); (H.-C.L.)
| | - Kai-Wen Hsu
- Research Center for Tumor Medical Science, China Medical University, Taichung 404, Taiwan;
- Graduate Institutes of New Drug Development, China Medical University, Taichung 404, Taiwan
| | - Kuo-Hung Huang
- Institute of Clinical Medicine, School of Medicine, National Yang-Ming University, Taipei 112, Taiwan; (K.-H.H.); (W.-L.F.)
- Department of Surgery, Taipei Veterans General Hospital, Taipei 112, Taiwan
| | - Wen-Liang Fang
- Institute of Clinical Medicine, School of Medicine, National Yang-Ming University, Taipei 112, Taiwan; (K.-H.H.); (W.-L.F.)
- Department of Surgery, Taipei Veterans General Hospital, Taipei 112, Taiwan
| | - Hsin-Chen Lee
- Department and Institute of Pharmacology, School of Medicine, National Yang-Ming University, Taipei 112, Taiwan; (L.-W.C.); (Y.-H.P.); (H.-C.L.)
| | - Chian-Feng Chen
- Cancer Progression Research Center, National Yang-Ming University, Taipei 112, Taiwan;
| | - Chen-Chung Liao
- Proteomics Research Center, National Yang-Ming University, Taipei 112, Taiwan;
| | - Rong-Hong Hsieh
- School of Nutrition and Health Sciences, College of Nutrition, Taipei Medical University, Taipei 110, Taiwan;
| | - Tien-Shun Yeh
- Institute of Anatomy and Cell Biology, School of Medicine, National Yang-Ming University, Taipei 112, Taiwan; (T.-T.H.); (J.-L.C.)
- Cancer Progression Research Center, National Yang-Ming University, Taipei 112, Taiwan;
- Institute of Biochemistry and Molecular Biology, National Yang-Ming University, Taipei 112, Taiwan
- Graduate Institute of Medical Sciences, College of Medicine, Taipei Medical University, Taipei 110, Taiwan
- Correspondence: ; Tel.: +886-2-2826-7070; Fax: +886-2-2821-2884
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14
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Jun DJ, Schumacher MM, Hwang S, Kinch LN, Grishin NV, DeBose-Boyd RA. Schnyder corneal dystrophy-associated UBIAD1 is defective in MK-4 synthesis and resists autophagy-mediated degradation. J Lipid Res 2020; 61:746-757. [PMID: 32188638 DOI: 10.1194/jlr.ra119000551] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 02/21/2020] [Indexed: 12/15/2022] Open
Abstract
The autosomal dominant disorder Schnyder corneal dystrophy (SCD) is caused by mutations in UbiA prenyltransferase domain-containing protein-1 (UBIAD1), which uses geranylgeranyl pyrophosphate (GGpp) to synthesize the vitamin K2 subtype menaquinone-4 (MK-4). SCD is characterized by opacification of the cornea, owing to aberrant build-up of cholesterol in the tissue. We previously discovered that sterols stimulate association of UBIAD1 with ER-localized HMG-CoA reductase, which catalyzes a rate-limiting step in the synthesis of cholesterol and nonsterol isoprenoids, including GGpp. Binding to UBIAD1 inhibits sterol-accelerated ER-associated degradation (ERAD) of reductase and permits continued synthesis of GGpp in cholesterol-replete cells. GGpp disrupts UBIAD1-reductase binding and thereby allows for maximal ERAD of reductase as well as ER-to-Golgi translocation of UBIAD1. SCD-associated UBIAD1 is refractory to GGpp-mediated dissociation from reductase and remains sequestered in the ER to inhibit ERAD. Here, we report development of a biochemical assay for UBIAD1-mediated synthesis of MK-4 in isolated membranes and intact cells. Using this assay, we compared enzymatic activity of WT UBIAD1 with that of SCD-associated variants. Our studies revealed that SCD-associated UBIAD1 exhibited reduced MK-4 synthetic activity, which may result from its reduced affinity for GGpp. Sequestration in the ER protects SCD-associated UBIAD1 from autophagy and allows intracellular accumulation of the mutant protein, which amplifies the inhibitory effect on reductase ERAD. These findings have important implications not only for the understanding of SCD etiology but also for the efficacy of cholesterol-lowering statin therapy, which becomes limited, in part, because of UBIAD1-mediated inhibition of reductase ERAD.
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Affiliation(s)
- Dong-Jae Jun
- Departments of Molecular Genetics,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Marc M Schumacher
- Departments of Molecular Genetics,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Seonghwan Hwang
- Departments of Molecular Genetics,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Lisa N Kinch
- Biophysics,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Nick V Grishin
- Biophysics,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046; Howard Hughes Medical Institute,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046
| | - Russell A DeBose-Boyd
- Departments of Molecular Genetics,University of Texas Southwestern Medical Center, Dallas, TX 75390-9046. mailto:
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15
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Renne MF, Klug YA, Carvalho P. Lipid droplet biogenesis: A mystery "unmixing"? Semin Cell Dev Biol 2020; 108:14-23. [PMID: 32192830 DOI: 10.1016/j.semcdb.2020.03.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2019] [Revised: 03/06/2020] [Accepted: 03/07/2020] [Indexed: 12/19/2022]
Abstract
Lipid droplets (LDs) are versatile organelles with central roles in lipid and energy metabolism in all eukaryotes. They primarily buffer excess fatty acids by storing them as neutral lipids, mainly triglycerides and steryl esters. The neutral lipids form a core, surrounded by a unique phospholipid monolayer coated with a defined set of proteins. Thus, the architecture of LDs sets them apart from all other membrane-bound organelles. The origin of LDs remained controversial for a long time. However, it has become clear that their biogenesis occurs at the endoplasmic reticulum (ER) and is a lipid driven process. LD formation is intiatied by the demixing of neutral lipids from membrane phospholipids, leading to the formation of a neutral lipid "lens" like structure between the leaflets of the ER bilayer. As this lens grows, it buds out of the membrane towards the cytosol to give rise to a LD. Recent biophysical and cell biological experiments indicate that LD biogenesis occurs at specific ER domains. These domains are enriched in various proteins required for normal LD formation and possibly have a lipid composition distinct from the remaining ER membrane. Here, we describe the prevailing model for LD formation and discuss recent insights on how proteins organize ER domains involved in LD biogenesis.
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Affiliation(s)
- Mike F Renne
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford, OX1 3RE, UK.
| | - Yoel A Klug
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford, OX1 3RE, UK.
| | - Pedro Carvalho
- Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford, OX1 3RE, UK.
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16
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Abstract
Lipid droplets are storage organelles at the centre of lipid and energy homeostasis. They have a unique architecture consisting of a hydrophobic core of neutral lipids, which is enclosed by a phospholipid monolayer that is decorated by a specific set of proteins. Originating from the endoplasmic reticulum, lipid droplets can associate with most other cellular organelles through membrane contact sites. It is becoming apparent that these contacts between lipid droplets and other organelles are highly dynamic and coupled to the cycles of lipid droplet expansion and shrinkage. Importantly, lipid droplet biogenesis and degradation, as well as their interactions with other organelles, are tightly coupled to cellular metabolism and are critical to buffer the levels of toxic lipid species. Thus, lipid droplets facilitate the coordination and communication between different organelles and act as vital hubs of cellular metabolism.
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Affiliation(s)
- James A Olzmann
- Department of Nutritional Sciences and Toxicology, University of California-Berkeley, Berkeley, CA, USA.
| | - Pedro Carvalho
- Sir William Dunn School of Pathology, University of Oxford, Oxford, UK.
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17
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Ma S, Sun W, Gao L, Liu S. Therapeutic targets of hypercholesterolemia: HMGCR and LDLR. Diabetes Metab Syndr Obes 2019; 12:1543-1553. [PMID: 31686875 PMCID: PMC6709517 DOI: 10.2147/dmso.s219013] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Accepted: 07/25/2019] [Indexed: 12/14/2022] Open
Abstract
Cholesterol homeostasis is critical and necessary for the body's functions. Hypercholesterolemia can lead to significant clinical problems, such as cardiovascular disease (CVD). 3-Hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR) and low-density lipoprotein cholesterol receptor (LDLR) are major points of control in cholesterol homeostasis. We summarize the regulatory mechanisms of HMGCR and LDLR, which may provide insight for new drug design and development.
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Affiliation(s)
- Shizhan Ma
- Department of Endocrinology and Metabolism, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan250021, People’s Republic of China
- Department of Endocrinology and Metabolism, Shandong Provincial Hospital Affiliated to Shandong University, Jinan250021, People’s Republic of China
| | - Wenxiu Sun
- Department of Pharmacy, Taishan Vocational College of Nursing, Taian271000, People’s Republic of China
| | - Ling Gao
- Department of Endocrinology and Metabolism, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan250021, People’s Republic of China
- Scientific Center, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan250021, People’s Republic of China
- Scientific Center, Shandong Provincial Hospital Affiliated to Shandong University, Jinan250021, People’s Republic of China
- Correspondence: Ling GaoScientific Center, Shandong Provincial Hospital Affiliated to Shandong University, 324 Jing 5 Road, Jinan, Shandong Province250021, People’s Republic of ChinaTel +86 531 6877 6910Email
| | - Shudong Liu
- Department of Endocrinology, Shandong Rongjun General Hospital, Jinan250013, People’s Republic of China
- Shudong LiuDepartment of Endocrinology, Shandong Rongjun General Hospital, 23 Jiefang Road, Jinan, Shandong Province250013, People’s Republic of ChinaTel +86 531 8238 2351Email
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18
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Zhang C, Liu P. The New Face of the Lipid Droplet: Lipid Droplet Proteins. Proteomics 2018; 19:e1700223. [DOI: 10.1002/pmic.201700223] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2018] [Revised: 08/13/2018] [Indexed: 12/20/2022]
Affiliation(s)
- Congyan Zhang
- National Laboratory of BiomacromoleculesCAS Center for Excellence in BiomacromoleculesInstitute of BiophysicsChinese Academy of Sciences Beijing 100101 China
- University of Chinese Academy of Sciences Beijing 100049 China
| | - Pingsheng Liu
- National Laboratory of BiomacromoleculesCAS Center for Excellence in BiomacromoleculesInstitute of BiophysicsChinese Academy of Sciences Beijing 100101 China
- University of Chinese Academy of Sciences Beijing 100049 China
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19
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Dropping in on lipid droplets: insights into cellular stress and cancer. Biosci Rep 2018; 38:BSR20180764. [PMID: 30111611 PMCID: PMC6146295 DOI: 10.1042/bsr20180764] [Citation(s) in RCA: 50] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Revised: 08/01/2018] [Accepted: 08/06/2018] [Indexed: 02/07/2023] Open
Abstract
Lipid droplets (LD) have increasingly become a major topic of research in recent years following its establishment as a highly dynamic organelle. Contrary to the initial view of LDs being passive cytoplasmic structures for lipid storage, studies have provided support on how they act in concert with different organelles to exert functions in various cellular processes. Although lipid dysregulation resulting from aberrant LD homeostasis has been well characterised, how this translates and contributes to cancer progression is poorly understood. This review summarises the different paradigms on how LDs function in the regulation of cellular stress as a contributing factor to cancer progression. Mechanisms employed by a broad range of cancer cell types in differentially utilising LDs for tumourigenesis will also be highlighted. Finally, we discuss the potential of targeting LDs in the context of cancer therapeutics.
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20
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Afonso MS, Machado RM, Lavrador MS, Quintao ECR, Moore KJ, Lottenberg AM. Molecular Pathways Underlying Cholesterol Homeostasis. Nutrients 2018; 10:E760. [PMID: 29899250 PMCID: PMC6024674 DOI: 10.3390/nu10060760] [Citation(s) in RCA: 78] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2018] [Revised: 06/10/2018] [Accepted: 06/11/2018] [Indexed: 01/14/2023] Open
Abstract
Cholesterol is an essential molecule that exerts pleiotropic actions. Although its presence is vital to the cell, its excess can be harmful and, therefore, sustaining cholesterol homeostasis is crucial to maintaining proper cellular functioning. It is well documented that high plasma cholesterol concentration increases the risk of atherosclerotic heart disease. In the last decades, several studies have investigated the association of plasma cholesterol concentrations and the risk of cardiovascular diseases as well as the signaling pathways involved in cholesterol homeostasis. Here, we present an overview of several mechanisms involved in intestinal cholesterol absorption, the regulation of cholesterol synthesis and uptake. We also discuss the importance of reverse cholesterol transport and transintestinal cholesterol transport to maintain cholesterol homeostasis and prevent atherosclerosis development. Additionally, we discuss the influence of dietary cholesterol on plasma cholesterol concentration and the new recommendations for cholesterol intake in a context of a healthy dietary pattern.
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Affiliation(s)
- Milessa Silva Afonso
- Marc and Ruti Bell Vascular Biology and Disease Program, Leon H. Charney Division of Cardiology, Department of Medicine, New York University School of Medicine, New York, NY 10016, USA.
| | - Roberta Marcondes Machado
- Laboratorio de Lipides (LIM 10), Hospital das Clínicas HCFMUSP, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo, SP 05403-000, Brazil.
| | - Maria Silvia Lavrador
- Laboratorio de Lipides (LIM 10), Hospital das Clínicas HCFMUSP, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo, SP 05403-000, Brazil.
| | - Eder Carlos Rocha Quintao
- Laboratorio de Lipides (LIM 10), Hospital das Clínicas HCFMUSP, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo, SP 05403-000, Brazil.
| | - Kathryn J Moore
- Marc and Ruti Bell Vascular Biology and Disease Program, Leon H. Charney Division of Cardiology, Department of Medicine, New York University School of Medicine, New York, NY 10016, USA.
- Department of Cell Biology, New York University School of Medicine, New York, NY 10016, USA.
| | - Ana Maria Lottenberg
- Laboratorio de Lipides (LIM 10), Hospital das Clínicas HCFMUSP, Faculdade de Medicina, Universidade de Sao Paulo, Sao Paulo, SP 05403-000, Brazil.
- Faculdade Israelita de Ciências da Saúde, Albert Einstein, São Paulo, SP 05403-000, Brazil.
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21
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Zhang J, Lan Y, Sanyal S. Modulation of Lipid Droplet Metabolism-A Potential Target for Therapeutic Intervention in Flaviviridae Infections. Front Microbiol 2017; 8:2286. [PMID: 29234310 PMCID: PMC5712332 DOI: 10.3389/fmicb.2017.02286] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Accepted: 11/06/2017] [Indexed: 12/21/2022] Open
Abstract
Lipid droplets (LDs) are endoplasmic reticulum (ER)-related dynamic organelles that store and regulate fatty acids and neutral lipids. They play a central role in cellular energy storage, lipid metabolism and cellular homeostasis. It has become evident that viruses have co-evolved in order to exploit host lipid metabolic pathways. This is especially characteristic of the Flaviviridae family, including hepatitis C virus (HCV) and several flaviviruses. Devoid of an appropriate lipid biosynthetic machinery of their own, these single-strand positive-sense RNA viruses can induce dramatic changes in host metabolic pathways to establish a favorable environment for viral multiplication and acquire essential components to facilitate their assembly and traffic. Here we have reviewed the current knowledge on the intracellular life cycle of those from the Flaviviridae family, with particular emphasis on HCV and dengue virus (DENV), and their association with the biosynthesis and metabolism of LDs, with the aim to identify potential antiviral targets for development of novel therapeutic interventions.
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Affiliation(s)
- Jingshu Zhang
- HKU-Pasteur Research Pole, School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China
| | - Yun Lan
- HKU-Pasteur Research Pole, School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China
| | - Sumana Sanyal
- HKU-Pasteur Research Pole, School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China.,School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China
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22
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Loregger A, Raaben M, Tan J, Scheij S, Moeton M, van den Berg M, Gelberg-Etel H, Stickel E, Roitelman J, Brummelkamp T, Zelcer N. Haploid Mammalian Genetic Screen Identifies UBXD8 as a Key Determinant of HMGCR Degradation and Cholesterol Biosynthesis. Arterioscler Thromb Vasc Biol 2017; 37:2064-2074. [PMID: 28882874 PMCID: PMC5671778 DOI: 10.1161/atvbaha.117.310002] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2017] [Accepted: 08/29/2017] [Indexed: 01/23/2023]
Abstract
Supplemental Digital Content is available in the text. Objective— The cellular demand for cholesterol requires control of its biosynthesis by the mevalonate pathway. Regulation of HMGCR (3-hydroxy-3-methylglutaryl coenzyme A reductase), a rate-limiting enzyme in this pathway and the target of statins, is a key control point herein. Accordingly, HMGCR is subject to negative and positive regulation. In particular, the ability of oxysterols and intermediates of the mevalonate pathway to stimulate its proteasomal degradation is an exquisite example of metabolically controlled feedback regulation. To define the genetic determinants that govern this process, we conducted an unbiased haploid mammalian genetic screen. Approach and Results— We generated human haploid cells with mNeon fused to endogenous HMGCR using CRISPR/Cas9 and used these cells to interrogate regulation of HMGCR abundance in live cells. This resulted in identification of known and new regulators of HMGCR, and among the latter, UBXD8 (ubiquitin regulatory X domain-containing protein 8), a gene that has not been previously implicated in this process. We demonstrate that UBXD8 is an essential determinant of metabolically stimulated degradation of HMGCR and of cholesterol biosynthesis in multiple cell types. Accordingly, UBXD8 ablation leads to aberrant cholesterol synthesis due to loss of feedback control. Mechanistically, we show that UBXD8 is necessary for sterol-stimulated dislocation of ubiquitylated HMGCR from the endoplasmic reticulum membrane en route to proteasomal degradation, a function dependent on its UBX domain. Conclusions— We establish UBXD8 as a previously unrecognized determinant that couples flux across the mevalonate pathway to control of cholesterol synthesis and demonstrate the feasibility of applying mammalian haploid genetics to study metabolic traits.
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Affiliation(s)
- Anke Loregger
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Matthijs Raaben
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Josephine Tan
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Saskia Scheij
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Martina Moeton
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Marlene van den Berg
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Hila Gelberg-Etel
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Elmer Stickel
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Joseph Roitelman
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Thijn Brummelkamp
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.)
| | - Noam Zelcer
- From the Department of Medical Biochemistry, Academic Medical Center of the University of Amsterdam, The Netherlands (A.L., J.T., S.S., M.M., M.v.d.B., N.Z.); Division of Biochemistry, The Netherlands Cancer Institute, Amsterdam (M.R., E.S., T.B.); CeMM Research Center for Molecular Medicine of the Austrian Academy of Sciences, Vienna (T.B.); Cancer GenomiCs.nl, Amsterdam, The Netherlands (T.B.); Bert W. Strassburger Lipid Center, Sheba Medical Center, Tel Hashomer, Israel (H.G.-E., J.R.); and Department of Human Genetics and Biochemistry, Sackler School of Medicine, Tel Aviv University, Israel (H.G.-E., J.R.).
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23
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Burr R, Ribbens D, Raychaudhuri S, Stewart EV, Ho J, Espenshade PJ. Dsc E3 ligase localization to the Golgi requires the ATPase Cdc48 and cofactor Ufd1 for activation of sterol regulatory element-binding protein in fission yeast. J Biol Chem 2017; 292:16333-16350. [PMID: 28821619 DOI: 10.1074/jbc.m117.802025] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Revised: 08/08/2017] [Indexed: 11/06/2022] Open
Abstract
Sterol regulatory element-binding proteins (SREBPs) in the fission yeast Schizosaccharomyces pombe regulate lipid homeostasis and the hypoxic response under conditions of low sterol or oxygen availability. SREBPs are cleaved in the Golgi through the combined action of the Dsc E3 ligase complex, the rhomboid protease Rbd2, and the essential ATPases associated with diverse cellular activities (AAA+) ATPase Cdc48. The soluble SREBP N-terminal transcription factor domain is then released into the cytosol to enter the nucleus and regulate gene expression. Previously, we reported that Cdc48 binding to Rbd2 is required for Rbd2-mediated SREBP cleavage. Here, using affinity chromatography and mass spectrometry experiments, we identified Cdc48-binding proteins in S. pombe, generating a list of many previously unknown potential Cdc48-binding partners. We show that the established Cdc48 cofactor Ufd1 is required for SREBP cleavage but does not interact with the Cdc48-Rbd2 complex. Cdc48-Ufd1 is instead required at a step prior to Rbd2 function, during Golgi localization of the Dsc E3 ligase complex. Together, these findings demonstrate that two distinct Cdc48 complexes, Cdc48-Ufd1 and Cdc48-Rbd2, are required for SREBP activation and low-oxygen adaptation in S. pombe.
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Affiliation(s)
- Risa Burr
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Diedre Ribbens
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Sumana Raychaudhuri
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Emerson V Stewart
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Jason Ho
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Peter J Espenshade
- From the Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
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24
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Printsev I, Curiel D, Carraway KL. Membrane Protein Quantity Control at the Endoplasmic Reticulum. J Membr Biol 2017; 250:379-392. [PMID: 27743014 PMCID: PMC5392169 DOI: 10.1007/s00232-016-9931-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2016] [Accepted: 09/28/2016] [Indexed: 02/07/2023]
Abstract
The canonical function of the endoplasmic reticulum-associated degradation (ERAD) system is to enforce quality control among membrane-associated proteins by targeting misfolded secreted, intra-organellar, and intramembrane proteins for degradation. However, increasing evidence suggests that ERAD additionally functions in maintaining appropriate levels of a subset of membrane-associated proteins. In this 'quantity control' capacity, ERAD responds to environmental cues to regulate the proteasomal degradation of specific ERAD substrates according to cellular need. In this review, we discuss in detail seven proteins that are targeted by the ERAD quantity control system. Not surprisingly, ERAD-mediated protein degradation is a key regulatory feature of a variety of ER-resident proteins, including HMG-CoA reductase, cytochrome P450 3A4, IP3 receptor, and type II iodothyronine deiodinase. In addition, the ERAD quantity control system plays roles in maintaining the proper stoichiometry of multi-protein complexes by mediating the degradation of components that are produced in excess of the limiting subunit. Perhaps somewhat unexpectedly, recent evidence suggests that the ERAD quantity control system also contributes to the regulation of plasma membrane-localized signaling receptors, including the ErbB3 receptor tyrosine kinase and the GABA neurotransmitter receptors. For these substrates, a proportion of the newly synthesized yet properly folded receptors are diverted for degradation at the ER, and are unable to traffic to the plasma membrane. Given that receptor abundance or concentration within the plasma membrane plays key roles in determining signaling efficiency, these observations may point to a novel mechanism for modulating receptor-mediated cellular signaling.
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Affiliation(s)
- Ignat Printsev
- Department of Biochemistry and Molecular Medicine, and UC Davis Comprehensive Cancer Center, UC Davis School of Medicine, Research Building III, Room 1100B, 4645 2nd Avenue, Sacramento, CA, 95817, USA
| | - Daniel Curiel
- Department of Biochemistry and Molecular Medicine, and UC Davis Comprehensive Cancer Center, UC Davis School of Medicine, Research Building III, Room 1100B, 4645 2nd Avenue, Sacramento, CA, 95817, USA
| | - Kermit L Carraway
- Department of Biochemistry and Molecular Medicine, and UC Davis Comprehensive Cancer Center, UC Davis School of Medicine, Research Building III, Room 1100B, 4645 2nd Avenue, Sacramento, CA, 95817, USA.
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25
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Welte MA, Gould AP. Lipid droplet functions beyond energy storage. Biochim Biophys Acta Mol Cell Biol Lipids 2017; 1862:1260-1272. [PMID: 28735096 PMCID: PMC5595650 DOI: 10.1016/j.bbalip.2017.07.006] [Citation(s) in RCA: 326] [Impact Index Per Article: 46.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 07/17/2017] [Accepted: 07/17/2017] [Indexed: 02/07/2023]
Abstract
Lipid droplets are cytoplasmic organelles that store neutral lipids and are critically important for energy metabolism. Their function in energy storage is firmly established and increasingly well characterized. However, emerging evidence indicates that lipid droplets also play important and diverse roles in the cellular handling of lipids and proteins that may not be directly related to energy homeostasis. Lipid handling roles of droplets include the storage of hydrophobic vitamin and signaling precursors, and the management of endoplasmic reticulum and oxidative stress. Roles of lipid droplets in protein handling encompass functions in the maturation, storage, and turnover of cellular and viral polypeptides. Other potential roles of lipid droplets may be connected with their intracellular motility and, in some cases, their nuclear localization. This diversity highlights that lipid droplets are very adaptable organelles, performing different functions in different biological contexts. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.
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Affiliation(s)
- Michael A Welte
- Department of Biology, University of Rochester, Rochester, NY, United States.
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26
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Joshi AS, Zhang H, Prinz WA. Organelle biogenesis in the endoplasmic reticulum. Nat Cell Biol 2017; 19:876-882. [DOI: 10.1038/ncb3579] [Citation(s) in RCA: 71] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2017] [Accepted: 06/21/2017] [Indexed: 12/16/2022]
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27
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Bersuker K, Olzmann JA. Establishing the lipid droplet proteome: Mechanisms of lipid droplet protein targeting and degradation. Biochim Biophys Acta Mol Cell Biol Lipids 2017. [PMID: 28627435 DOI: 10.1016/j.bbalip.2017.06.006] [Citation(s) in RCA: 94] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Lipid droplets (LDs) are ubiquitous, endoplasmic reticulum (ER)-derived organelles that mediate the sequestration of neutral lipids (e.g. triacylglycerol and sterol esters), providing a dynamic cellular storage depot for rapid lipid mobilization in response to increased cellular demands. LDs have a unique ultrastructure, consisting of a core of neutral lipids encircled by a phospholipid monolayer that is decorated with integral and peripheral proteins. The LD proteome contains numerous lipid metabolic enzymes, regulatory scaffold proteins, proteins involved in LD clustering and fusion, and other proteins of unknown functions. The cellular role of LDs is inherently determined by the composition of its proteome and alteration of the LD protein coat provides a powerful mechanism to adapt LDs to fluctuating metabolic states. Here, we review the current understanding of the molecular mechanisms that govern LD protein targeting and degradation. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.
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Affiliation(s)
- Kirill Bersuker
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, CA 94720, USA
| | - James A Olzmann
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, CA 94720, USA.
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28
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Scott Kiss R, Sniderman A. Shunts, channels and lipoprotein endosomal traffic: a new model of cholesterol homeostasis in the hepatocyte. J Biomed Res 2017; 31:95-107. [PMID: 28808191 PMCID: PMC5445212 DOI: 10.7555/jbr.31.20160139] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The liver directs cholesterol metabolism in the organism. All the major fluxes of cholesterol within the body involve the liver: dietary cholesterol is directed to the liver; cholesterol from peripheral cells goes to the liver; the liver is a major site of cholesterol synthesis for the organism; cholesterol is secreted from the liver within the bile, within apoB lipoproteins and translocated to nascent HDL. The conventional model of cholesterol homeostasis posits that cholesterol from any source enters a common, rapidly exchangeable pool within the cell, which is in equilibrium with a regulatory pool. Increased influx of cholesterol leads rapidly to decreased synthesis of cholesterol. This model was developed based on in vitro studies in the fibroblast and validated only for LDL particles. The challenges the liver must meet in vivo to achieve cholesterol homeostasis are far more complex. Our model posits that the cholesterol derived from three different lipoproteins endosomes has three different fates: LDL-derived cholesterol is largely recycled within VLDL with most of the cholesterol shunted through the hepatocyte without entering the exchangeable pool of cholesterol; high density lipoprotein-derived CE is transcytosed into bile; and chylomicron remnant-derived cholesterol primarily enters the regulatory pool within the hepatocyte. These endosomal channels represent distinct physiological pathways and hepatic homeostasis represents the net result of the outcomes of these distinct channels. Our model takes into account the distinct physiological challenges the hepatocyte must meet, underlie the pathophysiology of many of the apoB dyslipoproteinemias and account for the sustained effectiveness of therapeutic agents such as statins.
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Affiliation(s)
- Robert Scott Kiss
- Research Institute of the McGill University Health Centre, Montreal, Quebec H4A 3J1, Canada.,Department of Medicine, McGill University, Montreal, Quebec H4A 3J1, Canada
| | - Allan Sniderman
- Research Institute of the McGill University Health Centre, Montreal, Quebec H4A 3J1, Canada.,Department of Medicine, McGill University, Montreal, Quebec H4A 3J1, Canada
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29
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Meyers A, Chourey K, Weiskittel TM, Pfiffner S, Dunlap JR, Hettich RL, Dalhaimer P. The protein and neutral lipid composition of lipid droplets isolated from the fission yeast, Schizosaccharomyces pombe. J Microbiol 2017; 55:112-122. [PMID: 28120187 DOI: 10.1007/s12275-017-6205-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Revised: 10/04/2016] [Accepted: 10/20/2016] [Indexed: 12/17/2022]
Abstract
Lipid droplets consist of a core of neutral lipids surrounded by a phospholipid monolayer with bound proteins. Much of the information on lipid droplet function comes from proteomic and lipodomic studies that identify the components of droplets isolated from organisms throughout the phylogenetic tree. Here, we add to that important inventory by reporting lipid droplet factors from the fission yeast, Schizosaccharomyces pombe. Unique to this study was the fact that cells were cultured in three different environments: 1) late log growth phase in glucose-based media, 2) stationary phase in glucosebased media, and 3) late log growth phase in media containing oleic acid. We confirmed colocalization of major factors with lipid droplets using live-cell fluorescent microscopy. We also analyzed droplets from each of the three conditions for sterol ester (SE) and triacylglycerol (TAG) content, along with their respective fatty acid compositions. We identified a previously undiscovered lipid droplet protein, Vip1p, which affects droplet size distribution. The results provide further insight into the workings of these ubiquitous organelles.
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Affiliation(s)
- Alex Meyers
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN, 37996-2200, USA
| | - Karuna Chourey
- Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Taylor M Weiskittel
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN, 37996-2200, USA
| | - Susan Pfiffner
- Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, 37996, USA
| | - John R Dunlap
- Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, 37996, USA.,Advanced Microscopy and Imaging Center, University of Tennessee, Knoxville, TN, 37996, USA
| | | | - Paul Dalhaimer
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN, 37996-2200, USA. .,Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, 37996, USA. .,Institute of Biomedical Engineering, University of Tennessee, Knoxville, TN, 37996, USA.
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30
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Neal S, Mak R, Bennett EJ, Hampton R. A Cdc48 "Retrochaperone" Function Is Required for the Solubility of Retrotranslocated, Integral Membrane Endoplasmic Reticulum-associated Degradation (ERAD-M) Substrates. J Biol Chem 2017; 292:3112-3128. [PMID: 28077573 DOI: 10.1074/jbc.m116.770610] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2016] [Revised: 01/10/2017] [Indexed: 12/22/2022] Open
Abstract
A surprising feature of endoplasmic reticulum (ER)-associated degradation (ERAD) is the movement, or retrotranslocation, of ubiquitinated substrates from the ER lumen or membrane to the cytosol where they are degraded by the 26S proteasome. Multispanning ER membrane proteins, called ERAD-M substrates, are retrotranslocated to the cytosol as full-length intermediates during ERAD, and we have investigated how they maintain substrate solubility. Using an in vivo assay, we show that retrotranslocated ERAD-M substrates are moved to the cytoplasm as part of the normal ERAD pathway, where they are part of a solely proteinaceous complex. Using proteomics and direct biochemical confirmation, we found that Cdc48 serves as a critical "retrochaperone" for these ERAD-M substrates. Cdc48 binding to retrotranslocated, ubiquitinated ERAD-M substrates is required for their solubility; removal of the polyubiquitin chains or competition for binding by addition of free polyubiquitin liberated Cdc48 from retrotranslocated proteins and rendered them insoluble. All components of the canonical Cdc48 complex Cdc48-Npl4-Ufd1 were present in solubilized ERAD-M substrates. This function of the complex was observed for both HRD and DOA pathway substrates. Thus, in addition to the long known ATP-dependent extraction of ERAD substrates during retrotranslocation, the Cdc48 complex is generally and critically needed for the solubility of retrotranslocated ERAD-M intermediates.
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Affiliation(s)
- Sonya Neal
- Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California 92093
| | - Raymond Mak
- Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California 92093
| | - Eric J Bennett
- Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California 92093
| | - Randolph Hampton
- Division of Biological Sciences, Section of Cell and Developmental Biology, University of California, San Diego, La Jolla, California 92093.
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31
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Hantouche C, Williamson B, Valinsky WC, Solomon J, Shrier A, Young JC. Bag1 Co-chaperone Promotes TRC8 E3 Ligase-dependent Degradation of Misfolded Human Ether a Go-Go-related Gene (hERG) Potassium Channels. J Biol Chem 2016; 292:2287-2300. [PMID: 27998983 DOI: 10.1074/jbc.m116.752618] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Revised: 12/02/2016] [Indexed: 11/06/2022] Open
Abstract
Cardiac long QT syndrome type 2 is caused by mutations in the human ether a go-go-related gene (hERG) potassium channel, many of which cause misfolding and degradation at the endoplasmic reticulum instead of normal trafficking to the cell surface. The Hsc70/Hsp70 chaperones assist the folding of the hERG cytosolic domains. Here, we demonstrate that the Hsp70 nucleotide exchange factor Bag1 promotes hERG degradation by the ubiquitin-proteasome system at the endoplasmic reticulum to regulate hERG levels and channel activity. Dissociation of hERG complexes containing Hsp70 and the E3 ubiquitin ligase CHIP requires the interaction of Bag1 with Hsp70, but this does not involve the Bag1 ubiquitin-like domain. The interaction with Bag1 then shifts hERG degradation to the membrane-anchored E3 ligase TRC8 and its E2-conjugating enzyme Ube2g2, as determined by siRNA screening. TRC8 interacts through the transmembrane region with hERG and decreases hERG functional expression. TRC8 also mediates degradation of the misfolded hERG-G601S disease mutant, but pharmacological stabilization of the mutant structure prevents degradation. Our results identify TRC8 as a previously unknown Hsp70-independent quality control E3 ligase for hERG.
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Affiliation(s)
- Christine Hantouche
- From the Departments of Physiology and.,Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, Quebec H3G 0B1, Canada
| | - Brittany Williamson
- Biochemistry and.,Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, Quebec H3G 0B1, Canada
| | - William C Valinsky
- From the Departments of Physiology and.,Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, Quebec H3G 0B1, Canada
| | - Joshua Solomon
- From the Departments of Physiology and.,Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, Quebec H3G 0B1, Canada
| | - Alvin Shrier
- From the Departments of Physiology and .,Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, Quebec H3G 0B1, Canada
| | - Jason C Young
- Biochemistry and .,Groupe de Recherche Axé sur la Structure des Protéines, McGill University, Montreal, Quebec H3G 0B1, Canada
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32
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To M, Peterson CWH, Roberts MA, Counihan JL, Wu TT, Forster MS, Nomura DK, Olzmann JA. Lipid disequilibrium disrupts ER proteostasis by impairing ERAD substrate glycan trimming and dislocation. Mol Biol Cell 2016; 28:270-284. [PMID: 27881664 PMCID: PMC5231896 DOI: 10.1091/mbc.e16-07-0483] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2016] [Revised: 11/09/2016] [Accepted: 11/15/2016] [Indexed: 12/12/2022] Open
Abstract
The endoplasmic reticulum (ER) mediates the folding, maturation, and deployment of the secretory proteome. Proteins that fail to achieve their native conformation are retained in the ER and targeted for clearance by ER-associated degradation (ERAD), a sophisticated process that mediates the ubiquitin-dependent delivery of substrates to the 26S proteasome for proteolysis. Recent findings indicate that inhibition of long-chain acyl-CoA synthetases with triacsin C, a fatty acid analogue, impairs lipid droplet (LD) biogenesis and ERAD, suggesting a role for LDs in ERAD. However, whether LDs are involved in the ERAD process remains an outstanding question. Using chemical and genetic approaches to disrupt diacylglycerol acyltransferase (DGAT)-dependent LD biogenesis, we provide evidence that LDs are dispensable for ERAD in mammalian cells. Instead, our results suggest that triacsin C causes global alterations in the cellular lipid landscape that disrupt ER proteostasis by interfering with the glycan trimming and dislocation steps of ERAD. Prolonged triacsin C treatment activates both the IRE1 and PERK branches of the unfolded protein response and ultimately leads to IRE1-dependent cell death. These findings identify an intimate relationship between fatty acid metabolism and ER proteostasis that influences cell viability.
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Affiliation(s)
- Milton To
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720
| | - Clark W H Peterson
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720
| | - Melissa A Roberts
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720
| | - Jessica L Counihan
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720.,Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720.,Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720
| | - Tiffany T Wu
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720
| | - Mercedes S Forster
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720
| | - Daniel K Nomura
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720.,Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720.,Department of Molecular and Cell Biology, University of California, Berkeley, Berkeley, CA 94720
| | - James A Olzmann
- Department of Nutritional Sciences and Toxicology, University of California, Berkeley, Berkeley, CA 94720
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33
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Diacylglycerol acyltransferase-2 and monoacylglycerol acyltransferase-2 are ubiquitinated proteins that are degraded by the 26S proteasome. Biochem J 2016; 473:3621-3637. [DOI: 10.1042/bcj20160418] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2016] [Accepted: 08/16/2016] [Indexed: 01/20/2023]
Abstract
Acyl-CoA:1,2-diacylglycerol acyltransferase (DGAT)-2 is one of the two DGAT enzymes that catalyzes the synthesis of triacylglycerol, which is an important form of stored energy for eukaryotic organisms. There is currently limited information available regarding how DGAT2 and triacylglycerol synthesis are regulated. Recent studies have indicated that DGAT2 can be regulated by changes in gene expression. How DGAT2 is regulated post-transcriptionally remains less clear. In this study, we demonstrated that DGAT2 is a very unstable protein and is rapidly degraded in an ubiquitin-dependent manner via the proteasome. Many of the 25 lysines present in DGAT2 appeared to be involved in promoting its degradation. However, the six C-terminal lysines were the most important in regulating stability. We also demonstrated that acyl-CoA:monoacylglycerol acyltransferase (MGAT)-2, an enzyme with extensive sequence homology to DGAT2 that catalyzes the synthesis of diacylglycerol, was also ubiquitinated. However, MGAT2 was found to be much more stable than DGAT2. Interestingly, when co-expressed, MGAT2 appeared to stabilize DGAT2. Finally, we found that both DGAT2 and MGAT2 are substrates of the endoplasmic reticulum-associated degradation pathway.
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34
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Abstract
The endoplasmic reticulum is the port of entry for proteins into the secretory pathway and the site of synthesis for several important lipids, including cholesterol, triacylglycerol, and phospholipids. Protein production within the endoplasmic reticulum is tightly regulated by a cohort of resident machinery that coordinates the folding, modification, and deployment of secreted and integral membrane proteins. Proteins failing to attain their native conformation are degraded through the endoplasmic reticulum-associated degradation (ERAD) pathway via a series of tightly coupled steps: substrate recognition, dislocation, and ubiquitin-dependent proteasomal destruction. The same ERAD machinery also controls the flux through various metabolic pathways by coupling the turnover of metabolic enzymes to the levels of key metabolites. We review the current understanding and biological significance of ERAD-mediated regulation of lipid metabolism in mammalian cells.
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Affiliation(s)
- Julian Stevenson
- Program in Metabolic Biology, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720;
| | - Edmond Y Huang
- Program in Metabolic Biology, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720;
| | - James A Olzmann
- Program in Metabolic Biology, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720;
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35
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Hwang S, Hartman IZ, Calhoun LN, Garland K, Young GA, Mitsche MA, McDonald J, Xu F, Engelking L, DeBose-Boyd RA. Contribution of Accelerated Degradation to Feedback Regulation of 3-Hydroxy-3-methylglutaryl Coenzyme A Reductase and Cholesterol Metabolism in the Liver. J Biol Chem 2016; 291:13479-94. [PMID: 27129778 DOI: 10.1074/jbc.m116.728469] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Indexed: 11/06/2022] Open
Abstract
Accumulation of sterols in endoplasmic reticulum membranes stimulates the ubiquitination of 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGCR), which catalyzes a rate-limiting step in synthesis of cholesterol. This ubiquitination marks HMGCR for proteasome-mediated degradation and constitutes one of several mechanisms for feedback control of cholesterol synthesis. Mechanisms for sterol-accelerated ubiquitination and degradation of HMGCR have been elucidated through the study of cultured mammalian cells. However, the extent to which these reactions modulate HMGCR and contribute to control of cholesterol metabolism in whole animals is unknown. Here, we examine transgenic mice expressing in the liver the membrane domain of HMGCR (HMGCR (TM1-8)), a region necessary and sufficient for sterol-accelerated degradation, and knock-in mice in which endogenous HMGCR harbors mutations that prevent sterol-induced ubiquitination. Characterization of transgenic mice revealed that HMGCR (TM1-8) is appropriately regulated in the liver of mice fed a high cholesterol diet or chow diet supplemented with the HMGCR inhibitor lovastatin. Ubiquitination-resistant HMGCR protein accumulates in the liver and other tissues disproportionately to its mRNA, indicating that sterol-accelerated degradation significantly contributes to feedback regulation of HMGCR in vivo Results of these studies demonstrate that HMGCR is subjected to sterol-accelerated degradation in the liver through mechanisms similar to those established in cultured cells. Moreover, these studies designate sterol-accelerated degradation of HMGCR as a potential therapeutic target for prevention of atherosclerosis and associated cardiovascular disease.
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Affiliation(s)
- Seonghwan Hwang
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Isamu Z Hartman
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Leona N Calhoun
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Kristina Garland
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Gennipher A Young
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Matthew A Mitsche
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Jeffrey McDonald
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Fang Xu
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Luke Engelking
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
| | - Russell A DeBose-Boyd
- From the Department of Molecular Genetics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9046
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36
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Choudhary V, Golden A, Prinz WA. Keeping FIT, storing fat: Lipid droplet biogenesis. WORM 2016; 5:e1170276. [PMID: 27383728 DOI: 10.1080/21624054.2016.1170276] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Revised: 03/10/2016] [Accepted: 03/15/2016] [Indexed: 10/22/2022]
Abstract
All eukaryotes store excess lipids in organelles known as lipid droplets (LDs), which play central roles in lipid metabolism. Understanding LD biogenesis and metabolism is critical for understanding the pathophysiology of lipid metabolic disorders like obesity and atherosclerosis. LDs are composed of a core of neutral lipids surrounded by a monolayer of phospholipids that often contains coat proteins. Nascent LDs bud from the endoplasmic reticulum (ER) but the mechanism is not known. In this commentary we discuss our recent finding that a conserved family of proteins called fat storage-inducing transmembrane (FIT) proteins is necessary for LDs budding from the ER. In cells lacking FIT proteins, LDs remain in the ER membrane. C. elegans has a single FIT protein (FITM-2), which we found is essential; almost all homozygous fitm-2 animals die as larvae and those that survive to adulthood give rise to embryos that die as L1 and L2 larvae. Homozygous fitm-2 animals have a number of abnormalities including a significant decrease in intestinal LDs and dramatic defects in muscle development. Understanding how FIT proteins mediate LD biogenesis and what roles they play in lipid metabolism and development are fascinating challenges for the future.
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Affiliation(s)
- Vineet Choudhary
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health , Bethesda, MD, USA
| | - Andy Golden
- Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health , Bethesda, MD, USA
| | - William A Prinz
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health , Bethesda, MD, USA
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Choudhary V, Ojha N, Golden A, Prinz WA. A conserved family of proteins facilitates nascent lipid droplet budding from the ER. J Cell Biol 2016; 211:261-71. [PMID: 26504167 PMCID: PMC4621845 DOI: 10.1083/jcb.201505067] [Citation(s) in RCA: 200] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Visualization of nascent lipid droplets reveals that they form lens-like structures inside the ER membrane bilayer and that FIT proteins are necessary for lipid droplet protrusion toward the cytoplasm. Lipid droplets (LDs) are found in all cells and play critical roles in lipid metabolism. De novo LD biogenesis occurs in the endoplasmic reticulum (ER) but is not well understood. We imaged early stages of LD biogenesis using electron microscopy and found that nascent LDs form lens-like structures that are in the ER membrane, raising the question of how these nascent LDs bud from the ER as they grow. We found that a conserved family of proteins, fat storage-inducing transmembrane (FIT) proteins, is required for proper budding of LDs from the ER. Elimination or reduction of FIT proteins in yeast and higher eukaryotes causes LDs to remain in the ER membrane. Deletion of the single FIT protein in Caenorhabditis elegans is lethal, suggesting that LD budding is an essential process in this organism. Our findings indicated that FIT proteins are necessary to promote budding of nascent LDs from the ER.
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Affiliation(s)
- Vineet Choudhary
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
| | - Namrata Ojha
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
| | - Andy Golden
- Laboratory of Biochemistry and Genetics, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
| | - William A Prinz
- Laboratory of Cell and Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892
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38
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Nakatsukasa K, Kamura T. Subcellular Fractionation Analysis of the Extraction of Ubiquitinated Polytopic Membrane Substrate during ER-Associated Degradation. PLoS One 2016; 11:e0148327. [PMID: 26849222 PMCID: PMC4743956 DOI: 10.1371/journal.pone.0148327] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2015] [Accepted: 01/15/2016] [Indexed: 11/21/2022] Open
Abstract
During ER-associated degradation (ERAD), misfolded polytopic membrane proteins are ubiquitinated and retrotranslocated to the cytosol for proteasomal degradation. However, our understanding as to how polytopic membrane proteins are extracted from the ER to the cytosol remains largely unclear. To better define the localization and physical properties of ubiquitinated polytopic membrane substrates in vivo, we performed subcellular fractionation analysis of Ste6*, a twelve transmembrane protein that is ubiquitinated primarily by Doa10 E3 ligase in yeast. Consistent with previous in vitro studies, ubiquitinated Ste6* was extracted from P20 (20,000 g pellet) fraction to S20 (20,000 g supernatant) fraction in a Cdc48/p97-dependent manner. Similarly, Ubx2p, which recruits Cdc48/p97 to the ER, facilitated the extraction of Ste6*. By contrast, lipid droplet formation, which was suggested to be dispensable for the degradation of Hrd1-substrates in yeast, was not required for the degradation of Ste6*. Intriguingly, we found that ubiquitinated Ste6* in the S20 fraction could be enriched by further centrifugation at 100,000 g. Although it is currently uncertain whether ubiquitinated Ste6* in P100 fraction is completely free from any lipids, membrane flotation analysis suggested the existence of two distinct populations of ubiquitinated Ste6* with different states of membrane association. Together, these results imply that ubiquitinated Ste6* may be sequestered into a putative quality control sub-structure by Cdc48/p97. Fractionation assays developed in the present study provide a means to further dissect the ill-defined post-ubiquitination step during ERAD of polytopic membrane substrates.
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Affiliation(s)
- Kunio Nakatsukasa
- Division of Biological Sciences, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, Japan
- * E-mail: (KN); (TK)
| | - Takumi Kamura
- Division of Biological Sciences, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, Aichi, Japan
- * E-mail: (KN); (TK)
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39
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Khan SA, Wollaston-Hayden EE, Markowski TW, Higgins L, Mashek DG. Quantitative analysis of the murine lipid droplet-associated proteome during diet-induced hepatic steatosis. J Lipid Res 2015; 56:2260-72. [PMID: 26416795 DOI: 10.1194/jlr.m056812] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Indexed: 01/17/2023] Open
Abstract
Hepatic steatosis is characterized by the accumulation of lipid droplets (LDs), which are composed of a neutral lipid core surrounded by a phospholipid monolayer embedded with many proteins. Although the LD-associated proteome has been investigated in multiple tissues and organisms, the dynamic changes in the murine LD-associated proteome in response to obesity and hepatic steatosis have not been studied. We characterized the hepatic LD-associated proteome of C57BL/6J male mouse livers following high-fat feeding using isobaric tagging for relative and absolute quantification. Of the 1,520 proteins identified with a 5% local false discovery rate, we report a total of 48 proteins that were increased and 52 proteins that were decreased on LDs in response to high-fat feeding. Most notably, ribosomal and endoplasmic reticulum proteins were increased and extracellular and cytosolic proteins were decreased in response to high-fat feeding. Additionally, many proteins involved in fatty acid catabolism or xenobiotic metabolism were enriched in the LD fraction following high-fat feeding. In contrast, proteins involved in glucose metabolism and liver X receptor or retinoid X receptor activation were decreased on LDs of high-fat-fed mice. This study provides insights into unique biological functions of hepatic LDs under normal and steatotic conditions.
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Affiliation(s)
- Salmaan Ahmed Khan
- Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108
| | | | - Todd W Markowski
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455
| | - LeeAnn Higgins
- Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455
| | - Douglas G Mashek
- Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN 55108
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40
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Gao Q, Goodman JM. The lipid droplet-a well-connected organelle. Front Cell Dev Biol 2015; 3:49. [PMID: 26322308 PMCID: PMC4533013 DOI: 10.3389/fcell.2015.00049] [Citation(s) in RCA: 156] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Accepted: 07/24/2015] [Indexed: 12/19/2022] Open
Abstract
Our knowledge of inter-organellar communication has grown exponentially in recent years. This review focuses on the interactions that cytoplasmic lipid droplets have with other organelles. Twenty-five years ago droplets were considered simply particles of coalesced fat. Ten years ago there were hints from proteomics studies that droplets might interact with other structures to share lipids and proteins. Now it is clear that the droplets interact with many if not most cellular structures to maintain cellular homeostasis and to buffer against insults such as starvation. The evidence for this statement, as well as probes to understand the nature and results of droplet interactions, are presented.
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Affiliation(s)
- Qiang Gao
- Department of Pharmacology, University of Texas Southwestern Medical Center Dallas, TX, USA
| | - Joel M Goodman
- Department of Pharmacology, University of Texas Southwestern Medical Center Dallas, TX, USA
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41
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Moldavski O, Amen T, Levin-Zaidman S, Eisenstein M, Rogachev I, Brandis A, Kaganovich D, Schuldiner M. Lipid Droplets Are Essential for Efficient Clearance of Cytosolic Inclusion Bodies. Dev Cell 2015; 33:603-10. [PMID: 26004510 DOI: 10.1016/j.devcel.2015.04.015] [Citation(s) in RCA: 81] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2013] [Revised: 02/17/2015] [Accepted: 04/21/2015] [Indexed: 11/24/2022]
Abstract
Exposing cells to folding stress causes a subset of their proteins to misfold and accumulate in inclusion bodies (IBs). IB formation and clearance are both active processes, but little is known about their mechanism. To shed light on this issue, we performed a screen with over 4,000 fluorescently tagged yeast proteins for co-localization with a model misfolded protein that marks IBs during folding stress. We identified 13 proteins that co-localize to IBs. Remarkably, one of these IB proteins, the uncharacterized and conserved protein Iml2, exhibited strong physical interactions with lipid droplet (LD) proteins. Indeed, we here show that IBs and LDs are spatially and functionally linked. We further demonstrate a mechanism for IB clearance via a sterol-based metabolite emanating from LDs. Our findings therefore uncover a function for Iml2 and LDs in regulating a critical stage of cellular proteostasis.
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Affiliation(s)
- Ofer Moldavski
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Triana Amen
- Department of Cell and Developmental Biology, Alexander Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel
| | - Smadar Levin-Zaidman
- Electron Microscopy Unit, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Miriam Eisenstein
- Department of Chemical Research Support, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Ilana Rogachev
- Department for Biological Services, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Alexander Brandis
- Department for Biological Services, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Daniel Kaganovich
- Department of Cell and Developmental Biology, Alexander Silberman Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel.
| | - Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel.
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42
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Welte MA. As the fat flies: The dynamic lipid droplets of Drosophila embryos. Biochim Biophys Acta Mol Cell Biol Lipids 2015; 1851:1156-85. [PMID: 25882628 DOI: 10.1016/j.bbalip.2015.04.002] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Revised: 03/31/2015] [Accepted: 04/06/2015] [Indexed: 01/09/2023]
Abstract
Research into lipid droplets is rapidly expanding, and new cellular and organismal roles for these lipid-storage organelles are continually being discovered. The early Drosophila embryo is particularly well suited for addressing certain questions in lipid-droplet biology and combines technical advantages with unique biological phenomena. This review summarizes key features of this experimental system and the techniques available to study it, in order to make it accessible to researchers outside this field. It then describes the two topics most heavily studied in this system, lipid-droplet motility and protein sequestration on droplets, discusses what is known about the molecular players involved, points to open questions, and compares the results from Drosophila embryo studies to what it is known about lipid droplets in other systems.
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Affiliation(s)
- Michael A Welte
- Department of Biology University of Rochester, RC Box 270211, 317 Hutchison Hall, Rochester, NY 14627, USA.
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43
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Hashemi HF, Goodman JM. The life cycle of lipid droplets. Curr Opin Cell Biol 2015; 33:119-24. [PMID: 25703629 DOI: 10.1016/j.ceb.2015.02.002] [Citation(s) in RCA: 119] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2014] [Revised: 01/28/2015] [Accepted: 02/02/2015] [Indexed: 01/14/2023]
Abstract
Proteomic studies have revealed many potential functions of cytoplasmic lipid droplets, and recent activity has confirmed that these bona fide organelles are central not only for lipid storage and metabolism, but for development, immunity, and pathogenesis by several microbes. There has been a burst of recent activity on the assembly, maintenance and turnover of lipid droplets that reveals fresh insights. This review summarizes several novel findings in initiation of lipid droplet assembly, protein targeting, droplet fusion, and turnover of droplets through lipophagy.
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Affiliation(s)
- Hayaa F Hashemi
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9041, United States
| | - Joel M Goodman
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9041, United States.
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44
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Apodaca G, Brown WJ. Membrane traffic research: challenges for the next decade. Front Cell Dev Biol 2014; 2:52. [PMID: 25364759 PMCID: PMC4207031 DOI: 10.3389/fcell.2014.00052] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2014] [Accepted: 09/02/2014] [Indexed: 01/26/2023] Open
Affiliation(s)
- Gerard Apodaca
- The Renal-Electrolyte Division, Department of Medicine, University of Pittsburgh Pittsburgh, PA, USA
| | - William J Brown
- Molecular Biology and Genetics, Cornell University Ithaca, NY, USA
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45
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Abstract
To maintain cholesterol homeostasis, the processes of cholesterol metabolism are regulated at multiple levels including transcription, translation, and enzymatic activity. Recently, the regulation of protein stability of some key players in cholesterol metabolism has been characterized. More and more ubiquitin ligases have been identified including gp78, Hrd1, TRC8, TEB4, Fbw7, and inducible degrader of low density lipoprotein receptor. Their working mechanisms and physiological functions are becoming revealed. Here, we summarize the structure, substrates and function of these ubiquitin ligases. Their potential application in drug discovery is also discussed.
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Affiliation(s)
- Wei Jiang
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Bao-Liang Song
- Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China
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46
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Morris LL, Hartman IZ, Jun DJ, Seemann J, DeBose-Boyd RA. Sequential actions of the AAA-ATPase valosin-containing protein (VCP)/p97 and the proteasome 19 S regulatory particle in sterol-accelerated, endoplasmic reticulum (ER)-associated degradation of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. J Biol Chem 2014; 289:19053-66. [PMID: 24860107 DOI: 10.1074/jbc.m114.576652] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Accelerated endoplasmic reticulum (ER)-associated degradation (ERAD) of the cholesterol biosynthetic enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase results from its sterol-induced binding to ER membrane proteins called Insig-1 and Insig-2. This binding allows for subsequent ubiquitination of reductase by Insig-associated ubiquitin ligases. Once ubiquitinated, reductase becomes dislocated from ER membranes into the cytosol for degradation by 26 S proteasomes through poorly defined reactions mediated by the AAA-ATPase valosin-containing protein (VCP)/p97 and augmented by the nonsterol isoprenoid geranylgeraniol. Here, we report that the oxysterol 25-hydroxycholesterol and geranylgeraniol combine to trigger extraction of reductase across ER membranes prior to its cytosolic release. This conclusion was drawn from studies utilizing a novel assay that measures membrane extraction of reductase by determining susceptibility of a lumenal epitope in the enzyme to in vitro protease digestion. Susceptibility of the lumenal epitope to protease digestion and thus membrane extraction of reductase were tightly regulated by 25-hydroxycholesterol and geranylgeraniol. The reaction was inhibited by RNA interference-mediated knockdown of either Insigs or VCP/p97. In contrast, reductase continued to become membrane-extracted, but not cytosolically dislocated, in cells deficient for AAA-ATPases of the proteasome 19 S regulatory particle. These findings establish sequential roles for VCP/p97 and the 19 S regulatory particle in the sterol-accelerated ERAD of reductase that may be applicable to the ERAD of other substrates.
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Affiliation(s)
| | | | | | | | - Russell A DeBose-Boyd
- From the Departments of Molecular Genetics and the Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9046
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47
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Arrese EL, Saudale FZ, Soulages JL. Lipid Droplets as Signaling Platforms Linking Metabolic and Cellular Functions. Lipid Insights 2014; 7:7-16. [PMID: 25221429 PMCID: PMC4161058 DOI: 10.4137/lpi.s11128] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The main cells of the adipose tissue of animals, adipocytes, are characterized by the presence of large cytosolic lipid droplets (LDs) that store triglyceride (TG) and cholesterol. However, most cells have LDs and the ability to store lipids. LDs have a well-known central role in storage and provision of fatty acids and cholesterol. However, the complexity of the regulation of lipid metabolism on the surface of the LDs is still a matter of intense study. Beyond this role, a number of recent studies have suggested that LDs have major functions in other cellular processes, such as protein storage and degradation, infection, and immunity. Thus, our perception of LDs has been radically transformed from simple globules of fat to highly dynamic organelles of unexpected complexity. Here, we compiled some recent evidence supporting the emerging view that LDs act as platforms connecting a number of relevant metabolic and cellular functions.
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Affiliation(s)
- Estela L Arrese
- Department of Biochemistry and Molecular Biology; Oklahoma State University; Stillwater, OK, 74078, USA
| | - Fredy Z Saudale
- Department of Biochemistry and Molecular Biology; Oklahoma State University; Stillwater, OK, 74078, USA
| | - Jose L Soulages
- Department of Biochemistry and Molecular Biology; Oklahoma State University; Stillwater, OK, 74078, USA
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48
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Abstract
Lipid droplets (LDs) are an intracellular organelle, consisting of a neutral lipid core covered by a monolayer of phospholipids and proteins. It primarily mediates lipid storage, metabolism, and transportation. Recently, research of LDs has emerged as a rapidly developing field due to the strong linkage between ectopic lipid accumulation and metabolic syndromes. Recently, more than 30 proteomic studies of isolated LDs have identified many important LD proteins that have highlighted and have also predicted the potential biological roles of the organelle, motivating the field to develop quite rapidly. This chapter summarizes methods used in proteomic studies for three representative species reported and discusses their advantages and disadvantages. We believe that this chapter provides useful information and methods for future LD proteomic studies especially for LDs in other species.
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49
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Zafar S, Coates DE, Cullinan MP, Drummond BK, Milne T, Seymour GJ. Zoledronic acid and geranylgeraniol regulate cellular behaviour and angiogenic gene expression in human gingival fibroblasts. J Oral Pathol Med 2014; 43:711-21. [PMID: 24762323 DOI: 10.1111/jop.12181] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 02/11/2014] [Indexed: 11/28/2022]
Abstract
The mevalonate pathway (MVP) and the anti-angiogenic effect of bisphosphonates have been shown to play a role in the pathogenesis of bisphosphonate-related osteonecrosis of the jaw (BRONJ). This study determined the effect of the bisphosphonate, zoledronic acid and the replenishment of the MVP by geranylgeraniol on human gingival fibroblasts. Cell viability, apoptosis, morphological analysis using transmission electron microscopy, and gene expression for vascular endothelial growth factor A, bone morphogenic protein 2, ras homologue gene family member B, epiregulin and interferon-alpha were conducted. Results showed cellular viability was decreased in the presence of zoledronic acid and the co-addition of zoledronic acid with geranylgeraniol restored cell viability to control levels. Caspase 3/7 was detected in zoledronic-acid-treated cells indicating apoptosis. Transmission electron microscopy revealed dilation of the rough endoplasmic reticulum with zoledronic acid and the appearance of multiple lipid-like vesicles following the addition of geranylgeraniol. Zoledronic acid significantly (P < 0.05, FR > ± 2) up-regulated vascular endothelial growth factor A, bone morphogenic protein 2, ras homologue gene family member B and epiregulin at one or more time points but not interferon-alpha. Addition of geranylgeraniol resulted in a reduction in the expression of all five genes compared with zoledronic-acid-treated human gingival fibroblasts. The study concluded geranylgeraniol partially reversed the effects of zoledronic acid in human gingival fibroblasts both at the cellular and genetic levels, suggesting the regulation of these genes is mediated via the mevalonate pathway.
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Affiliation(s)
- S Zafar
- Faculty of Dentistry, Sir John Walsh Research Institute, University of Otago, Dunedin, New Zealand
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50
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Wilfling F, Haas JT, Walther TC, Farese RV. Lipid droplet biogenesis. Curr Opin Cell Biol 2014; 29:39-45. [PMID: 24736091 DOI: 10.1016/j.ceb.2014.03.008] [Citation(s) in RCA: 288] [Impact Index Per Article: 28.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2014] [Revised: 03/18/2014] [Accepted: 03/19/2014] [Indexed: 11/28/2022]
Abstract
Lipid droplets (LDs) are found in most cells, where they play central roles in energy and membrane lipid metabolism. The de novo biogenesis of LDs is a fascinating, yet poorly understood process involving the formation of a monolayer bound organelle from a bilayer membrane. Additionally, large LDs can form either by growth of existing LDs or by the combination of smaller LDs through several distinct mechanisms. Here, we review recent insights into the molecular process governing LD biogenesis and highlight areas of incomplete knowledge.
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Affiliation(s)
- Florian Wilfling
- Yale School of Medicine, Department of Cell Biology, New Haven, CT, USA
| | - Joel T Haas
- Gladstone Institute of Cardiovascular Disease, San Francisco, CA, USA; Department of Biochemistry and Biophysics, University of California-San Francisco, CA, USA
| | - Tobias C Walther
- Yale School of Medicine, Department of Cell Biology, New Haven, CT, USA.
| | - Robert V Farese
- Gladstone Institute of Cardiovascular Disease, San Francisco, CA, USA; Department of Biochemistry and Biophysics, University of California-San Francisco, CA, USA; Department of Medicine, University of California-San Francisco, CA, USA.
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